1. Field of the Invention
This invention relates to polycrystalline diamond constructions used for subterranean drilling applications and, more particularly, to polycrystalline diamond constructions engineered having a controlled gradient content of catalyst/binder material for purposes of providing optimized properties of abrasion resistance and thermal stability, while maintaining a desired degree of fracture toughness, impact resistance, and resistance to delamination when compared to conventional polycrystalline diamond constructions.
2. Background of the Invention
Polycrystalline diamond (PCD) materials known in the art are formed from diamond grains or crystals and a catalyst material, and are synthesized by high pressure-high temperature (HP/HT) processes. Such PCD materials are known for having a high degree of wear resistance, making them a popular material choice for use in such industrial applications as cutting tools for machining, and wear and/or cutting elements in subterranean mining and drilling, where such high levels of wear or abrasion resistance are desired. In such applications, conventional PCD materials may be provided in the form of a surface layer or an entire material body to impart desired levels of wear and abrasion resistance thereto.
Traditionally, PCD cutting elements used in such applications are formed by applying one or more layers of such PCD material to, or forming a body of such PCD material, for attachment with a suitable substrate material. Example PCD cutting elements known in the art may include a substrate, a PCD surface layer or body, and optionally one or more transition or intermediate layers to improve the bonding between and/or provide transition properties between the PCD surface layer or body and the underlying substrate support layer. Substrates used in such cutting element applications include carbides such as cemented tungsten carbide (WC—Co).
Such conventional PCD material comprises about 10 percent by volume of a catalyst material to facilitate intercrystalline bonding between the diamond grains, and to bond the PCD material to the underlying substrate and/or transition layer. Metals conventionally employed as the catalyst are often selected from the group of solvent metal catalysts including cobalt, iron, nickel, and mixtures thereof, found in Group VIII of the Periodic Table.
The amount of catalyst material used to form PCD materials represents a compromise between desired properties of toughness and hardness/wear resistance in the resulting sintered diamond body. While a higher metal catalyst content typically increases the toughness of a resulting PCD material, such higher metal catalyst content also decreases the hardness and corresponding wear and abrasion resistance of the PCD material. Also, as PCD materials are formed with increasing diamond volume fraction there is an increase in thermal mismatch between the sintered PCD and the tungsten carbide substrate creating higher residual stresses near the interface between these materials which residual stresses are undesired as they may promote cracking and/or delamination within the PCD construction.
Thus, these inversely affected desired properties ultimately limit the flexibility of being able to provide PCD materials having desired levels of both wear resistance and toughness to meet the service demands of particular applications, such as cutting and/or wear elements used in subterranean drilling devices. Additionally, when variables are selected to increase the wear resistance of the PCD material, typically brittleness also increases, thereby reducing the toughness and impact resistance of the PCD material.
A further desired property of PCD constructions used for certain applications is that they be thermally stable during wear or cutting operating conditions. A problem known to exist with conventional PCD materials is that they are vulnerable to thermal degradation when exposed to elevated temperatures during cutting and/or wear applications. This vulnerability results from the differential that exists between the thermal expansion characteristics of the metal catalyst disposed interstitially within the PCD material and the thermal expansion characteristics of the intercrystalline bonded diamond. Such differential thermal expansion is known to start at temperatures as low as 400° C., may induce thermal stresses that may be detrimental to the intercrystalline bonding of diamond, and may eventually result in the formation of cracks that may make the PCD structure vulnerable to failure. Accordingly, such behavior is not desirable.
Another form of thermal degradation known to exist with conventional PCD materials is one that is also related to the presence of the metal catalyst in the interstitial regions of the PCD material and the adherence of the solvent metal catalyst to the diamond crystals. Specifically, the solvent metal catalyst is known to cause an undesired catalyzed phase transformation in diamond (converting it to carbon monoxide, carbon dioxide, or graphite) with increasing temperature, thereby limiting practical use of the PCD material to about 750° C.
It is, therefore, desirable that a PCD material be developed that displays improved and optimized combined properties of wear and abrasion resistance, low residual stress, and thermal stability for use in complex wear environments, when compared to conventional PCD materials, while not sacrificing desired properties of toughness, impact resistance, and delamination resistance, making them well suited for use in the same applications.